Numerous fine adjustment boring features have been employed identified in the trade as "Easy Set", "Microdex", "Flexidex" and "Camset" employing differential screws, set screws and other microadjustable units to accomplish fine adjustment on larger diameters. One example of a fine adjusting head relevant to the present invention is sold under the tradename Komet KFK, MICROADJUSTABLE BORING HEAD. The head includes a tool slide radially adjustable by means of a feed screw extending through the slide with a nut and dial on opposite ends rotatable to effect radial adjustment of the slide. A vernier scale on the dial provides accurate calibration and a substantial adjustment range comparable to that of the present invention.